Test article



United States Patent C 3,453,180 TEST ARTICLE Joseph Wilfred Fraser, Jr., Elkhart, Ind., and Roger Lee Atkinson, Three Rivers, Mich., assignors to Miles Laboratories, Inc., Elkhart, Ind., a corporation of Indiana No Drawing. Filed Aug. 2, 1965, Ser. No. 476,703 Int. Cl. C12k 1/04; G01n 33/16 U.S. Cl. 195-99 1 Claim ABSTRACT OF THE DISCLOSURE The present invention relates to a test article useful for detecting glucose in a fluid, such as urine. More particularly, the invention relates to a test article having an improved composition which provides more accurate quantitative determination of glucose levels in urine than prior art test articles.

The detection of glucose in body fluids, such as urine or blood, as well as the determination of its concentration therein is of great importance to diabetic patients who must control their diets so as to regulate their sugar intake and who must frequently be guided in this regard by a regular check on glucose in their body fluids. A test article for qualitatively and quantitatively determining glucose can also 'be used efliciently in routine analyses of body fluids in hospitals and physicians oflices, in diabetes detection screening programs, in the differentiation of glucose from other sugars, and the like.

Because early diagnosis and continued control are so important in diabetes, a glucose test, to be of greatest value, must be conveniently rapid, simple enough to serve the clinician, and sensitive enough to reflect variations in the patients condition.

One test article that has been used in the prior art for the detection of glucose in fluids, such as urine, is described in U.S. Patent No. 3,123,443, issued to R. R. Smeby on Mar. 3, 1964. This prior art test article was particularly useful in detecting glucose in urine. It contained a test mixture impregnated on a bibulous material. The impregnated mixture contained glucose oxidase, peroxidase, o-tolidine dihydrochloride as an indicator, a citric acid-sodium citrate bufler mixture, sodium alginate, gelatin and a polyoxyethylene s-orbitan mono-oleate surfactant.

The principles underlying the basic reactions of enzyme tests for glucose are well known. Glucose oxidase catalyzes the aerobic oxidation of glucose to produce gluconic acid and hydrogen peroxide. A substance having peroxidative activity is then capable of inducing the oxidation of an indicator, such as o-tolidine dihydrochloride, in the presence of the hydrogen peroxide formed by the glucose oxidase. The degree of oxidation of the indicator, and thus its resulting shade of color, is thus directly related to the amount of glucose present in the sample being tested.

In the test mixture described in the above-mentioned patent, sodium alginate was employed to aid in maintaining stability of the glucose response characteristics of the test article during storage. Gelatin was employed to aid in producing the desired color response to glucose through- 3,453,180 Patented July 1, 1969 out the test area of the test article. The polyoxyethylene sorbitan mono-oleate surfactant was employed to aid in proper mixing with an aqueous alcohol solvent to form a solution containing the test mixture which could be substantially uniformly impregnated into a bibulous material base member.

While the above described prior art test article was a distinct advance in the art, it had some disadvantages in manufacture and in use. The prior art test mixture was not completely soluble in the aqueous alcohol solvent used to prepare the impregnating solution. When a bibulous base member was impregnated with this solution and then dried, this tended to produce a test article having a minor amount of visibly discrete particles on the surface of the impregnated portion of the test article. Such particles were undesirable from an esthetic viewpoint. When the test mixture solution is applied to a bibulous base member through a small diameter orifice, these undissolved solid particles have a tendency to clog the orifice and thus interfere with proper application of the test mixture. The prior art test article also did not provide suflicient gradations in the color spectrum produced by the indicator to afford desired differentiation in glucose levels at the low glucose concentrations.

It is an object of the present invention to provide a test article having a reagent-impregnated area for detecting glucose in fluids which is free from visibly discrete particles.

It is a further object of the present invention to provide a test article for detecting glucose in fluids which has improved detection characteristics over prior art test articles.

In accordance With the present invention, a test article for detecting glucose in a fluid is provided which comprises a bibulous material containing impregnated therein the dried residue of a liquid mixture which comprises a liquid enzyme system having glucose oxidase activity, a substance having peroxidative activity, a long-chain polymer of 3,6-anhydro-D-galactose and sulfated D-galactose residues, polyvinyl pyrrolidone, a derivative of an interpolymer of methyl vinyl ether and maleic anhydride, said derivative being selected from the class consisting of the acid form and the partial ester form, a citric acid-sodium citrate buffer system, o-tolidine dihydrochloride, and sodium lauroyl sarcosinate. The principal points of novelty in the above composition are the inclusion of liquid glucose oxidase, the long-chain galactose polymer, polyvinyl pyrrolidone, the interpolymer of methyl vinyl ether and maleic anhydride, and the sodium lauroyl sarcosinate. Such items have replaced the powdered glucose oxidase, sodium alginate, gelatin an polyoxyethylene sorbitan mono-oleate of the prior art compositions and have provided improved results in the manufacture and use of a test article for detecting glucose in a fluid.

The glucose oxidase employed in the production of the test article of the present invention is a liquid glucose oxidase substantially free of catalase. Such material is available under the trademark DeeO Liquid from the Miles Chemical Co. The liquid glucose oxidase is conveniently employed in a form containing about 1000 glucose oxidase units per ml. of liquid glucose oxidase. A glucose oxidase unit is well known in the enzyme art to represent the amount of glucose oxidase that will catalyze the oxidation of a glucose substrate containing 3.3 Weight percent glucose monohydrate with 10 microliters of oxygen per minute at 35 C. and pH 5.1 over a 15 minute period. It should be understood that any liquid enzyme system having glucose oxidase activity can be used in the present invention.

The substances having peroxidative activity which can be used in the present invention can be chosen from various organicand inorganic sources. The various plant peroxidases, such as horseradish peroxidase or potato peroxidase, can be used. There can also be used small measured portions, capable of producing little coloration or a definitely predetermined color background effect, of such substances as normal whole blood, red blood cells alone, lyophilized whole blood and like substances having peroxidative activity. Inorganic compounds having peroxidative activity, such as mixtures of potassium iodide and sodium molybdate, as well as other iodides, such as sodium and ammonium iodides, and other molybdates, such as potassium and ammonium dates, can be used. In addition, urohemin and a number of other porphydrin substances having peroxidative activity can be used. Other substances which are not enzymes but have peroxidative activity include such compounds as iron sulfocyanate, iron tannate, ferrous ferrocyanide, potassium chromic sulfate and the like.

The interpolymer of methyl vinyl ether and maleic anhydride useful in the formation of the novel test article of the present invention is an equimolar reaction product of methyl vinyl ether and maleic anhydride and is represented by the following formula:

wherein n is a positive number and is of suflicient value to provide a composition having a specific viscosity of about 0.1 to about 3.5 as measured on a 1 weight percent solution in methyl ethyl ketone. This interpolymer is marketed commercially under the trademark Gantrez AN" by the General Aniline and Film Corporation. When the interpolymer is dissolved in water, it forms an acid derivative having the following unit formula:

I I (I320 OH OH When the interpolymer is dissolved in an alcohol having the formula ROH, wherein R represents the organic moiety, it forms a partial ester derivative having the following unit formula:

l til Since the test articles of the present invention are prepared from aqueous alcohol solutions, the test composition in the final product will contain either the acid derivative or the partial ester derivative or a mixture of said derivatives.

The preferred indicator used in the present invention is o-tolidine dihydrochloride. This indicator provides various shades of blue when it is oxdized by peroxidase in the presence of hydrogen peroxide obtained from the glucose being analyzed.

The composition employed in the present novel test article to measure glucose in urine, for example, should be maintained at a pH of from about 4 to about 6, preferably about pH 5. This pH is maintained by the citric acidsodium citrate buffer system.

The presence of the above described interpolymer derivatives along with polyvinyl pyrrolidone having, for example, an average molecular weight of about 40,000, and a long-chain polymer of 3,6-anhydro-D-galactose and sulfated D-galactose residues greatly enhances the color formed by the indicator when it is oxidized. This color enhancement aids in color differentiation, especially when low levels of glucose (about 0.1 weight percent) are be ing detected. This is particularly important in obtaining a glucose test which can detect the presence of an incipient diabetic condition, for example.

The long-chain polymer of 3,6-anhydro-D-galactose and sulfated D-galactose residues is available commercially from Marine Colloids Inc. under the trademark Viscarin. The long-chain polymer has a molecular weight of several hundred thousand.

A surfactant is employed in the present invention to obtain desired solution characteristics. The preferred surfactant is sodium lauroyl sarcosinate marketed under the trademark Sarkosyl NL30 by Geigy Chemical Co.

A dye is preferably used to mask any discolorations in the bibulous base member and also to provide a background color which is in contrast to the colors produced by the indicator. A red background color is preferably employed herein to contrast with the blue colors produced by o-toluidine dihydrochloride when glucose is detected. This composition thus produces an overall spectrum from red (no glucose) to violet (about 0.1 weight percent glucose) to purple (about 0.250.5 weight percent glucose) to dark purple (over about 0.5 weight percent glucose). FD&C Red No. 3 (CI. 45430) or a mixture of FD&C Red No. 3 and FD&C Red No. 4 (CI. 14700) is conveniently employed for this background color.

The novel test articles are prepared by impregnating a bibulous material base member with the above described composition dissolved in an aqueous alcohol medium. This impregnation can be achieved either by dipping the bibulous material into the liquid composition or by flowing the liquid composition into contacts with the surface of the bibulous material. The resulting impregnated bibulous material is then suitably dried.

The invention will be further described in the following example.

EXAMPLE To 2750 ml. of distilled water at C. were added 25 g. of a long-chain polymer of 3,6-anhydro-D-galactose and sulfated D-galactose residues. This material was marketed under the trademark of Viscarin" by Marine Colloids Inc. The mixture was stirred until the solids dissolved. To this solution were then added 250 g. of polyvinyl pyrrolidone having an average molecular weight of about 40,000 and the mixture was stirred until the solids dissolved. The solution was cooled to 25 C. and 250 ml. of denatured ethanol were added.

A dye solution was obtained by mixing 0.9 g. of FD&C Red No. 4 dyestuff (C.I. 14700) and 2.0 g. of FD&C Red No. 3 dyestutf (CI. 45430) in 450 ml. of distilled water at room temperature. This dye solution was then mixed with the above solution to form Solution A.

An indicator solution was prepared by mixing 50 g. of o-tolidine dihydrochloride in 550 ml. of distilled water at C.

A buffer solution was prepared by dissolving 154.2 g. of anhydrous citric acid and 679.2 g. of sodium citrate in 2080 ml. of distilled water at room temperature. To this buffer solution were then added 1800 ml. of denatured ethanol. The alcoholic buffer solution was then mixed with the indicator solution and the resulting solution was mixed with Solution A to form Solution B.

An interpolymer solution was prepared by mixing 75 g. of Gantrez AN 139, an interpolymer of methyl vinyl ether and maleic anhydride marketed by General Aniline and Film Corporation, with 1500 ml. of distilled water at 95 C. After reaction between the interpolymer and water was completed, the solution was cooled to 25 C. and distilled water was added to restore the original solution volume. This solution was then added to Solution B to from Solution C.

A surfactant solution was prepared by mixing 25 g. of sodium lauroyl sarcosinate, marketed under the trademark of Sarkosyl NL 30 by Geigy Chemical C0,, with 250 ml. of distilled water. This solution was then added to Solution C to form Solution D.

An enzyme solution was prepared by mixing 5 g. of horseradish peroxidase and 760 ml. of liquid glucose oxidase having an activity of about 1000 glucose oxidase units per ml. The liquid glucose oxidase was obtained from the Miles Chemical Co. under the trademark DeeO Liquid. This enzyme solution was then added to Solution D to form Solution E.

A strip of bibulous filter paper was then passed through Solution E to impregnate the bibulous filter paper with the reagent mixture of Solution E. The impregnated filter paper was then dried at about 100 C. for minutes. The dried impregnated test area of the resulting test strip had a uniform color and texture and had no visibly discrete particles on its surface. It thus had an esthetically pleasing appearance.

The above prepared reagent-impregnated bibulous test strip was then used to test glucose response in urine. It provided improved color differentiation, especially at low glucose levels, as compared with the color response of prior art glucose test articles. This test strip exhibited the desired color response to glucose uniformly throughout the impregnated test area and also exhibited a high degree of stability which afforded extended shelf life.

In summary, the present invention relates to an improved test article which is especially useful for measuring glucose levels in urine. This test article comprises a bibulous material impregnated with the dried residue of a liquid composition including a liquid glucose oxidase, peroxidase, polyvinyl pyrrolidone, a derivative of an interpolymer of methyl vinyl ether and maleic anhydride, long-chain galactose polymer derivative, citric acid-sodium citrate buffer, o-tolidine dihydrochloride indicator, and sodium lauroyl sarcosinate surfactant.

What is claimed is:

1. A test article for detecting glucose in urine which I comprises a bibulous material containing impregnated therein the dried residue of a liquid mixture which comprises a liquid enzyme system having glucose oxidase activity, a substance having peroxidative activity, citric acidsodium citrate buffer system capable of maintainng a pH from about 4 to about 6, o-tolidine dihydrochloride, polyvinyl pyrrolidone, a derivative of an interpolymer of equimolar amounts of methyl vinyl ether and maleic anhydride having a specific viscosity of about 0.1 to about 3.5 as measured on a 1 weight percent solution in methyl ethyl ketone, said derivative being selected from the class consisting of the acid form and the partial ester form, sodium lauroyl sarcosinate, and a long-chain polymer of 3,6-anhydro-D-galactose and sulfated D-galactose residues.

References Cited UNITED STATES PATENTS 3,016,292 1/1962 Bauer et al 23253 3,123,443 3/1964 Smeby 23-253 3,298,789 1/1967 Mast 23-253 MORRIS O. WOLK, Primary Examiner.

E. A. KATZ, Assistant Examiner.

US. Cl. X.R. 

